1. Field of the Invention
The present invention relates to an apparatus for testing the tightness of the seating of a plug in a hole and removing inadequately secured plugs. The invention has application to plugs disposed in limited access locations wherein there are severe constraints on movement in the plug-removing direction. The invention has particular application to the testing and removal of upflow conversion plugs in thermal shield nuclear plants.
2. Description of the Prior Art
In a nuclear reactor the core assembly is disposed within a cylindrical core barrel and, more particularly, is confined within a zig-zag array of baffle plates which are spaced inwardly from the core barrel side wall. The space between the baffle plates and the core barrel side wall is closed by a plurality of vertically spaced-apart former plates.
In a typical "downflow" cooling arrangement, cooling water is pumped downwardly along the outside of the core barrel, the water flowing through a plurality of circumferentially spaced-apart flow holes in the core barrel disposed just below the top former plate, into the region between the core barrel side wall and the baffle plates. This latter flow then passes down through holes in the former plates and beneath the lower end of the baffle plates into the core region to join with water flowing up into the core region through holes in the bottom of the core barrel. In this "downflow" arrangement, there is high pressure water on the outside of the baffle plates and low pressure water on the inside, due to pressure loss during the travel through the fuel core assembly. The baffle plates are simply a series of bolted-together plates and the high pressure water on the outside of these plates causes jet streams to flow through cracks between the baffle plates into the core, which can damage the fuel assemblies.
In order to correct this problem, there is performed what is known as an "upflow conversion" on the reactor. In this conversion process the flow holes in the core barrel side wall are plugged with expandable plugs, and holes are drilled in the top former plate. Thus, the cooling water can no longer enter through the flow holes in the core barrel side wall. Rather it flows down along the outside of the core barrel, up through the holes in the bottom of the core barrel and then under the baffle plates and then upwardly through the region between the baffle plates and the core barrel side wall, exiting through the new holes in the top former plate, this upflowing water being under much lower pressure than the downflowing water.
Occasionally it becomes necessary to test the flow hole plugs to see if they have been properly installed so as to withstand a radial pull-out force of 6,000 lbs. (approximately equivalent to a pressure of 1,750 psig applied to the plug from within the core barrel). This presents a problem in nuclear reactors with thermal shields, which are cylindrical structures surrounding the core barrel side wall coaxially therewith. Typically, the thermal shield is spaced radially outwardly from the core barrel a very slight distance of approximately 1.5 inches, and the only access to the flow hole plugs is downwardly through this narrow annular space. Heretofore, there have been no means available for gaining access to the flow hole plugs through this narrow annular space and exerting on the plugs the necessary pull-out force.